Perhaps the difficulty you're having in explaining the differences between MDs and DOs to lay people lies in the fact that whatever differences exist between the two professions are a little too wishy-washy for most people to accept.
Realize that any differences today between the allopathic and osteopathic professions are essentially intangible or confused with chiropractic.
Look at the hard differences between allopathic and osteopathic medicine first.
1) Osteopathic physicians attend one of nineteen colleges of osteopathic medicine and MD physicians attend one of one-hundred and twenty-six schools of medicine.
2) Osteopathic physicians have their own professional organization, the AOA, but many are also members of the AMA -- probably confuses people.
3) Osteopathic physicians have their own system of postgraduate training (residency) that is not open to MDs, but roughly 2/3 of graduating DOs choose to enter the postgraduate training programs (residencies) of MDs -- probably confuses people.
4) Osteopathic physicians are licensed in all fifty-states of the USA to practice medicine and surgery in a limitless scope that is equal to that of MDs.
5) Osteopathic physicians are trained to practice osteopathic manipulative medicine, but some MDs have sought advanced training in this and have even enrolled in structured programs (as at KCOM).
But the proponents of DO = MD + OMT miss what may be the real difference between MDs and DOs, something that's been taught to generations of DOs and has become, essentially, the battle-cry of the new AOA campaign. "DOs treat people, not just symptoms." HOLY COW! Can you be more vague? The implication here to people who are well-read on the subject is that osteopathic physicians take a whole-person, whole-body approach that excludes nothing and tends to lack a focus. More importantly the battle-cry does little to explain to people why DOs are different as, anybody knows, MDs don't just treat symptoms either and with 2/3 of DOs going through MD residency programs where the "osteopathic concept" is decidedly lost, you can bet that more DOs are practicing like MDs. And with the MDs being the older of the two, and with their supposed treatment of "just symptoms," funny that it's worked for so long without a peep from the then-non-existent osteopathic community. 🙂
Anyway you'll find that the hard differences between MDs and DOs do little to explain to lay people why DOs are a separate profession, other than that there's a different set of letters at the end of the doctor's name. But you'll also find that the more wishy-washy differences (DOs treat people, not just symptoms) escape practically everyone.